Longitudinally-adjustable bone anchors and related methods

ABSTRACT

Longitudinally-adjustable bone anchors and related methods are disclosed herein. The ability to adjust a bone anchor longitudinally can allow the surgeon to bring an implanted bone anchor up to the rod instead of or in addition to bringing the rod down to the bone anchor, which can simplify or eliminate the rod contouring step and reduce or eliminate reduction forces. For example, the surgeon can use a pre-bent rod or put “ideal contours” into a rod, lay the rod across a series of bone anchors, and adjust each bone anchor longitudinally to meet the rod. As another example, coarse adjustment of the fixation system can be achieved by contouring the rod and then fine adjustments can be made by bringing each bone anchor up or down to the rod. Various adjustment mechanisms are disclosed, including bone anchors with telescoping portions and bone anchors with risers or spacers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 15/370,078,filed Dec. 6, 2016, which is hereby incorporated by reference in itsentirety.

FIELD

Longitudinally-adjustable bone anchors and related methods are disclosedherein.

BACKGROUND

Fixation systems can be used in orthopedic surgery to maintain a desiredspatial relationship between multiple bones or bone fragments. Forexample, various conditions of the spine, such as fractures,deformities, and degenerative disorders, can be treated by attaching aspinal fixation system to one or more vertebrae. Such systems typicallyinclude a spinal fixation element, such as a rigid or flexible rod orplate, that is coupled to the vertebrae by attaching the element tovarious anchoring devices, such as screws, hooks, or wires. Onceinstalled, the fixation system holds the vertebrae in a desired positionuntil healing or spinal fusion can occur, or for some other period oftime.

Placing the fixation system typically requires that one or more rods bebent or contoured very accurately to fit within several bone anchorsimplanted along the spine. The rods are typically bent in threedimensions and may need to be bent to match adjacent rods that areworking in concert, to accommodate a deformity, or to account forgravity and soft tissue forces. In addition, contouring a rod too manytimes can reduce the fatigue life of the rod. In view of these and otherchallenges, the precise contouring of a rod to approximate the rod to aseries of bone anchors is a time consuming and artful procedure.

It can also be a very important procedure. The alignment of a patient'svertebrae is usually a key output of the surgery and the patient'swellbeing can depend on post-operative alignment. The rods apply thecorrective loads to the spine and are what hold the alignmentpost-surgery while healing or fusion takes place. If the rods are notcontoured accurately, too much pre-stress can be applied to the boneanchors, which can result in mal-union or mal-alignment. For example,when a rod is improperly contoured, significant reduction forces musttypically be applied to bring the rod into alignment with the boneanchors. These forces can cause unequal loading or loosening of the boneanchors at the anchor-bone interface, which can result in instrument orconstruct failure, non-union, or pain. As shown in FIG. 1A, applicationof significant reduction forces, e.g., using a reduction instrument ofthe type shown in FIG. 1B, to bone anchors at intermediate levels of afixation construct can cause damage to the osseous threads and looseningor dislocation of the bone anchors. A similar phenomenon can occur atthe end levels of the construct. For example, performing a cantileverrod reduction maneuver to restore lordosis (as shown in FIG. 1C) canresult in significant reduction and recoil forces at the screw-boneinterfaces (as shown in FIG. 1D), which ultimately can lead to failureat the anchor-bone interface with loosening or dislocation of the boneanchor (as shown in FIG. 1E).

Application of significant reduction forces can also cause iatrogeniccentral or foraminal stenosis by segmental translation of one vertebrain relation to another. For example, as shown in FIGS. 1F-1G,rod-to-anchor reduction can cause sagittal plane translation of onevertebra (e.g., C4 as shown) relative to an adjacent vertebra (e.g., C5as shown), pinching the nerve tissue and resulting in pain, weakness,numbness, loss of function, or other symptoms.

Some surgeons may try to limit the reduction forces by backing out thebone anchor a few turns to meet the rod, however this can have the sameeffect of compromising bone purchase and weakening the anchor-boneinterface.

SUMMARY

Longitudinally-adjustable bone anchors and related methods are disclosedherein. The ability to adjust a bone anchor longitudinally can allow thesurgeon to bring an implanted bone anchor up to the rod instead of or inaddition to bringing the rod down to the bone anchor, which can simplifyor eliminate the rod contouring step and reduce or eliminate reductionforces. For example, the surgeon can use a pre-bent rod or put “idealcontours” into a rod, lay the rod across a series of bone anchors, andadjust each bone anchor longitudinally to meet the rod. As anotherexample, coarse adjustment of the fixation system can be achieved bycontouring the rod and then fine adjustments can be made by bringingeach bone anchor up or down to the rod. Various adjustment mechanismsare disclosed, including bone anchors with telescoping portions and boneanchors with risers or spacers.

In some embodiments, a longitudinally-adjustable bone anchor includes areceiver member that defines a rod-receiving recess; and a shank havinginner and outer telescoping portions, the outer telescoping portion ofthe shank including a bone-engaging thread and defining an inner cavity,the inner telescoping portion including a shaft disposed in the cavityof the outer telescoping portion and a head that movably couples theshank to the receiver member; wherein the inner and outer telescopingportions are longitudinally-adjustable relative to one another to adjusta length of the bone anchor.

The inner telescoping portion can be constrained from rotating axiallyrelative to the outer telescoping portion. The inner telescoping portioncan be threaded into the cavity of the outer telescoping portion. Thebone anchor can include a locking element configured to selectivelyprevent distal movement of the inner telescoping portion relative to theouter telescoping portion, to prevent proximal movement of the innertelescoping portion relative to the outer telescoping portion, or toprevent both proximal and distal movement of the inner telescopingportion relative to the outer telescoping portion. The locking elementcan include one or more biased teeth configured to project radiallyinward from an inner sidewall of the cavity to engage the shaft as theshaft is moved proximally within the cavity. The locking element caninclude a threaded engagement between the inner and outer telescopingportions. The locking element can include a locking ring disposed aroundthe shaft of the inner telescoping portion and configured to engageratchet teeth spaced longitudinally along an inner surface of thecavity. The cavity can include proximal and distal portions separated byan annular projection. The shaft can be biased distally relative to theouter telescoping portion by a spring disposed between the annularprojection and a shoulder formed on the shaft. The locking element caninclude one or more tabs extending from the receiver member. The tabscan be configured to wedge between the inner and outer telescopingportions when a distally-directed force is applied to the tabs.Tightening a closure mechanism to the receiver member can apply adistally-directed force to the tabs. Each of the tabs can have a foldedposition and a deployed position, the tabs in the deployed positionbeing configured to contact the outer telescoping portion and supportthe receiver member in an elevated position relative to the outertelescoping portion.

In some embodiments, a longitudinally-adjustable bone anchor includes areceiver member that defines a rod-receiving channel having a first rodseat; a threaded shank movably coupled to the receiver member; and aspacer disposed in the rod-receiving channel of the receiver member andhaving a distal surface that contacts the first rod seat and a proximalsurface that defines a second rod seat spaced a distance apart from thefirst rod seat.

The first rod seat can be defined by opposed U-shaped recesses formed inthe receiver member. The distal surface of the spacer can be a sectionof a cylinder. The proximal surface of the spacer can be a section of acylinder. The spacer can include one or more protrusions that engage anouter sidewall of the receiver member to prevent translation of thespacer relative to the receiver member along a longitudinal axis of thespacer. The protrusions can extend from the distal surface of thespacer. The protrusions can be convexly curved. The protrusions caninclude inwardly-facing planar surfaces that engage correspondingoutwardly-facing planar surfaces of the receiver member. The spacer caninclude opposed planar sidewalls connecting the proximal and distalsurfaces of the spacer that engage respective opposed planar sidewallsof the rod-receiving channel.

In some embodiments, a bone fixation method includes implanting a boneanchor in a bone of a patient, the bone anchor having a proximal portionthat includes a rod seat configured to receive a fixation rod thereinand a distal portion configured to engage bone, the bone anchor having alength L defined between the rod seat and a distal-most tip of the boneanchor; positioning a fixation rod with respect to the bone anchor suchthat the fixation rod is offset proximally from the rod seat; andextending the length L of the bone anchor to reduce the offset betweenthe fixation rod and the rod seat.

In some embodiments, the length L is adjusted independently of adjustinga position of the distal portion of the bone anchor relative to thebone. In some embodiments, the distal portion of the bone anchorincludes a thread that is threaded into the bone and the length L isadjusted without moving the thread relative to the bone. In someembodiments, the length L is adjusted independently of adjusting anangle between the proximal and distal portions of the bone anchor. Insome embodiments, the length L is adjusted at a location other than aninterface between the proximal and distal portions of the bone anchor.The distal portion of the bone anchor can include inner and outertelescoping portions and adjusting the length L can include moving theinner telescoping portion proximally relative to the outer telescopingportion. The method can include locking at least one of proximalmovement, distal movement, and both proximal and distal movement of theinner telescoping portion relative to the outer telescoping portion viaa locking element. The locking element can include at least one of:biased teeth configured to deploy from a cavity of the outer telescopingportion to engage the inner telescoping portion; a threaded engagementbetween the inner and outer telescoping portions; a locking ringdisposed around the inner telescoping portion and engaged with ratchetteeth formed in a cavity of the outer telescoping portion; tabsconfigured to wedge between the inner and outer telescoping portionswhen a distally-directed force is applied to the tabs; and tabs having afolded position and a deployed position, the tabs in the deployedposition being configured to contact the outer telescoping portion andsupport the proximal portion of the bone anchor in an elevated positionrelative to the outer telescoping portion. Adjusting the length L caninclude inserting a spacer between the rod and the proximal portion ofthe receiver member, the rod seat being defined by a proximal surface ofthe spacer. The method can include selecting the spacer from a kit of aplurality of spacers, each of the plurality of spacers having adifferent height and the selected spacer having a height correspondingto a desired degree of extension of the length L.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a sectional schematic view of a human spine instrumented witha fixation construct, showing dislocation of intermediate level boneanchors;

FIG. 1B is a side view of a reduction instrument, a spinal rod, and abone anchor;

FIG. 1C is a sectional schematic view of a human spine instrumented witha fixation construct, showing a cantilever rod reduction maneuver;

FIG. 1D is a sectional schematic view of the human spine and fixationconstruct of FIG. 1C, showing reduction and recoil forces at thescrew-bone interfaces;

FIG. 1E is a sectional schematic view of the human spine and fixationconstruct of FIG. 1C, showing dislocation of an end level bone anchor;

FIG. 1F is a sectional schematic view of a human spine instrumented witha fixation construct, before reducing a rod into an intermediate boneanchor;

FIG. 1G is a sectional schematic view of the human spine and fixationconstruct of FIG. 1F, after reducing the rod into the intermediate boneanchor, showing stenosis caused by said reduction;

FIG. 1H is an exploded perspective view of a prior art bone anchor;

FIG. 1I is a sectional perspective view of the bone anchor of FIG. 1H;

FIG. 1J is a perspective view of a receiver member of the bone anchor ofFIG. 1H, shown with reduction tabs;

FIG. 2A is a sectional schematic side view of alongitudinally-adjustable bone anchor and a spinal rod, shown before rodreduction;

FIG. 2B is another sectional schematic side view of the bone anchor ofFIG. 2A, shown at an intermediate stage of rod reduction;

FIG. 2C is another sectional schematic side view of the bone anchor ofFIG. 2A, shown in a longitudinally-adjusted configuration;

FIG. 2D is another sectional schematic side view of the bone anchor ofFIG. 2A, shown in a final configuration;

FIG. 3A is a sectional schematic side view of alongitudinally-adjustable bone anchor;

FIG. 3B is another sectional schematic side view of the bone anchor ofFIG. 3A, shown in a longitudinally-adjusted configuration;

FIG. 3C is another sectional schematic side view of the bone anchor ofFIG. 3A, shown with a spinal rod seated in the bone anchor;

FIG. 3D is another sectional schematic side view of the bone anchor ofFIG. 3A, shown in a final configuration;

FIG. 4A is a sectional perspective view of a longitudinally-adjustablebone anchor and a spinal rod;

FIG. 4B is a sectional perspective detail view of the distal end of thebone anchor of FIG. 4A;

FIG. 4C is a sectional perspective detail view of the proximal end ofthe bone anchor of FIG. 4A;

FIG. 5A is a sectional schematic side view of alongitudinally-adjustable bone anchor and a spinal rod, shown before rodreduction;

FIG. 5B is another sectional schematic side view of the bone anchor ofFIG. 5A, shown at an intermediate stage of rod reduction;

FIG. 5C is another sectional schematic side view of the bone anchor ofFIG. 5A, shown in a longitudinally-adjusted configuration;

FIG. 5D is another sectional schematic side view of the bone anchor ofFIG. 5A, shown in a final configuration;

FIG. 5E is another sectional schematic side view of the bone anchor ofFIG. 5A, shown before longitudinal adjustment;

FIG. 5F is another sectional schematic side view of the bone anchor ofFIG. 5A, shown after longitudinal adjustment;

FIG. 6A is a perspective view of a longitudinally-adjustable bone anchorand a spinal rod;

FIG. 6B is a perspective view of a spacer that can be used with the boneanchor of FIG. 6A;

FIG. 6C is a perspective view of another spacer that can be used withthe bone anchor of FIG. 6A, having a height greater than that of thespacer of FIG. 6B; and

FIG. 6D is a perspective view of a closure mechanism and cap of the boneanchor of FIG. 6A.

DETAILED DESCRIPTION

Longitudinally-adjustable bone anchors and related methods are disclosedherein. The ability to adjust a bone anchor longitudinally can allow thesurgeon to bring an implanted bone anchor up to the rod instead of or inaddition to bringing the rod down to the bone anchor, which can simplifyor eliminate the rod contouring step and reduce or eliminate reductionforces. For example, the surgeon can use a pre-bent rod or put “idealcontours” into a rod, lay the rod across a series of bone anchors, andadjust each bone anchor longitudinally to meet the rod. As anotherexample, coarse adjustment of the fixation system can be achieved bycontouring the rod and then fine adjustments can be made by bringingeach bone anchor up or down to the rod. Various adjustment mechanismsare disclosed, including bone anchors with telescoping portions and boneanchors with risers or spacers.

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the structure, function,manufacture, and use of the devices and methods disclosed herein. One ormore examples of these embodiments are illustrated in the accompanyingdrawings. Those skilled in the art will understand that the devices andmethods specifically described herein and illustrated in theaccompanying drawings are non-limiting exemplary embodiments. Thefeatures illustrated or described in connection with one exemplaryembodiment may be combined with the features of other embodiments.

Prior Art Bone Anchor

FIGS. 1H-1J illustrate a prior art bone anchor 100 with various featuresthat can be included in the bone anchors 200, 300, 400, 500, 600described below. It will be appreciated that the illustrated bone anchor100 is exemplary and that the bone anchors 200, 300, 400, 500, 600described below can include additional or alternative features.

The illustrated bone anchor 100 includes an anchor portion or shank 102,a head or receiver member 104 for receiving a spinal fixation element,such as a spinal rod 106, to be coupled to the anchor portion 102, and afastener or closure mechanism 108 to capture a spinal fixation elementwithin the receiver member and fix the spinal fixation element withrespect to the receiver member. The anchor portion 102 includes aproximal head 110 and a distal shaft 112 configured to engage bone. Thereceiver member 104 has a proximal end having a pair of spaced apartarms 114A, 114B defining a recess or channel 116 therebetween and adistal end having a distal end surface defining an opening through whichat least a portion of the anchor portion 102 extends. The closuremechanism 108 can be positionable between and can engage the arms 114A,114B to capture a spinal fixation element, e.g., a spinal rod 106,within the receiver member 104 and fix the spinal fixation element withrespect to the receiver member.

The proximal head 110 of the anchor portion 102 is generally in theshape of a truncated sphere having a planar proximal surface and anapproximately spherically-shaped distal surface. The illustrated boneanchor 100 is a polyaxial bone screw designed for posterior implantationin the pedicle or lateral mass of a vertebra. The proximal head 110 ofthe anchor portion 102 engages the distal end of the receiver member 104in a ball and socket like arrangement in which the proximal head and thedistal shaft 112 can pivot relative to the receiver member. The distalsurface of the proximal head 110 of the anchor portion 102 and a matingsurface within the distal end of the receiver member 104 can have anyshape that facilitates this arrangement, including, for example,spherical (as illustrated), toroidal, conical, frustoconical, and anycombinations of these shapes.

The distal shaft 112 of the anchor portion 102 can be configured toengage bone and, in the illustrated embodiment, includes an externalbone engaging thread. The thread form for the distal shaft 112,including the number of threads, the pitch, the major and minordiameters, and the thread shape, can be selected to facilitateconnection with bone. Exemplary thread forms are disclosed in U.S.Patent Application Publication No. 2011/0288599, filed on May 18, 2011,and in U.S. Patent Application Publication No. 2013/0053901, filed onAug. 22, 2012, both of which are hereby incorporated by referenceherein. The distal shaft 112 can also include other structures forengaging bone, including a hook. The distal shaft 112 of the anchorportion 102 can be cannulated, having a central passage or cannulaextending the length of the anchor portion to facilitate delivery of theanchor portion over a guidewire in, for example, minimally-invasiveprocedures. Other components of the bone anchor 100, including, forexample, the closure mechanism 108, the receiver member 104, and thecompression member or cap 118 (discussed below) can be cannulated orotherwise have an opening to permit delivery over a guidewire. Thedistal shaft 112 can also include one or more sidewall openings orfenestrations that communicate with the cannula to permit bone in-growthor to permit the dispensing of bone cement or other materials throughthe anchor portion 102. The sidewall openings can extend radially fromthe cannula through the sidewall of the distal shaft 112. Exemplarysystems for delivering bone cement to the bone anchor 100 andalternative bone anchor configurations for facilitating cement deliveryare described in U.S. Patent Application Publication No. 2010/0114174,filed on Oct. 29, 2009, which is hereby incorporated by referenceherein. The distal shaft 112 of the anchor portion 102 can also becoated with materials to permit bone growth, such as, for example,hydroxyapatite, and the bone anchor 100 can be coated partially orentirely with anti-infective materials, such as, for example, tryclosan.

The proximal end of the receiver member 104 includes a pair of spacedapart arms 114A, 114B defining a U-shaped recess 116 therebetween forreceiving a spinal fixation element, e.g., a spinal rod 106. Each of thearms 114A, 114B can extend from the distal end of the receiver member104 to a free end. The outer surfaces of each of the arms 114A, 114B caninclude a feature, such as a recess, dimple, notch, projection, or thelike, to facilitate connection of the receiver member 104 toinstruments. For example, the outer surface of each arm 114A, 114B caninclude an arcuate groove at the respective free end of the arms. Suchgrooves are described in more detail in U.S. Pat. No. 7,179,261, issuedon Feb. 20, 2007, which is hereby incorporated by reference herein.

The distal end of the receiver member 104 includes a distal end surfacewhich is generally annular in shape defining a circular opening throughwhich at least a portion of the anchor portion 102 extends. For example,the distal shaft 112 of the anchor portion 102 can extend through theopening.

The anchor portion 102 can be selectively fixed relative to the receivermember 104. Prior to fixation, the anchor portion 102 is movablerelative to the receiver member 104 within a cone of angulationgenerally defined by the geometry of the distal end of the receivermember and the proximal head 110 of the anchor portion 102. The boneanchor 100 can be a favored angle screw, for example as disclosed inU.S. Pat. No. 6,974,460, issued on Dec. 13, 2005, and in U.S. Pat. No.6,736,820, issued on May 18, 2004, both of which are hereby incorporatedby reference herein. Alternatively, the bone anchor 100 can be aconventional (non-biased) polyaxial screw in which the anchor portion102 pivots in the same amount in every direction.

The spinal fixation element, e.g., the spinal rod 106, can eitherdirectly contact the proximal head 110 of the anchor portion 102 or cancontact an intermediate element, e.g., a compression member 118. Thecompression member 118 can be positioned within the receiver member 104and interposed between the spinal rod 106 and the proximal head 110 ofthe anchor portion 102 to compress the distal outer surface of theproximal head into direct, fixed engagement with the distal innersurface of the receiver member 104. The compression member 118 caninclude a pair of spaced apart arms 120A and 120B defining a U-shapedseat 122 for receiving the spinal rod 106 and a distal surface forengaging the proximal head 110 of the anchor portion 102.

The proximal end of the receiver member 104 can be configured to receivea closure mechanism 108 positionable between and engaging the arms 114A,114B of the receiver member. The closure mechanism 108 can be configuredto capture a spinal fixation element, e.g., a spinal rod 106, within thereceiver member 104, to fix the spinal rod relative to the receivermember, and to fix the anchor portion 102 relative to the receivermember. The closure mechanism 108 can be a single set screw having anouter thread for engaging an inner thread provided on the arms 114A,114B of the receiver member 104. In the illustrated embodiment, however,the closure mechanism 108 includes an outer set screw 124 operable toact on the compression member 118 and an inner set screw 126 operable toact on the rod 106. Various other closure mechanisms 108 can be usedinstead or in addition, such as a nut that extends around an outercircumference of the receiver member 104, a cap or fastener that slidesonto the receiver member from the side, or a cap or fastener that locksto the receiver member by quarter-turn rotation. The receiver member 104can include, can be formed integrally with, or can be coupled to one ormore extension tabs 128 (shown in FIG. 1J) that extend proximally fromthe receiver member 104 to functionally extend the length of the arms114A, 114B. The extension tabs 128 can facilitate installation andassembly of a fixation or stabilization construct and can be removedprior to completing a surgical procedure.

The bone anchor 100 can be used with a spinal fixation element such asrigid spinal rod 106. Alternatively, the spinal fixation element can bea dynamic stabilization member that allows controlled mobility betweenthe instrumented vertebrae.

In use, the bone anchor 100 can be assembled such that the distal shaft112 extends through the opening in the distal end of the receiver member104 and the proximal head 110 of the anchor portion 102 is received inthe distal end of the receiver member 104. A driver instrument can befitted with the anchor portion 102 to drive the anchor portion intobone. The compression member 118 can be positioned within the receivermember 104 such that the arms 120A, 120B of the compression member arealigned with the arms 114A, 114B of the receiver member 104 and thelower surface of the compression member 118 is in contact with theproximal head 110 of the anchor portion 102. A spinal fixation element,e.g., the spinal rod 106, can be located in the recess 116 of thereceiver member 104. The closure mechanism 108 can be engaged with theinner thread provided on the arms 114A, 114B of the receiver member 104.A torsional force can be applied to the outer set screw 124 to move itwithin the recess 116 so as to force the compression member 118 onto theproximal head 110 of the anchor portion 102, thereby locking the angularposition of the anchor portion 102 relative to the receiver member 104.A torsional force can be applied to the inner set screw 126 to force thespinal rod 106 into engagement with the compression member 118 andthereby fix the spinal rod 106 relative to the receiver member 104.

The bone anchors 200, 300, 400, 500, 600 described below can beconfigured to operate in conjunction with, or can include any of thefeatures of, bone anchors of the type described above or other typesknown in the art. Exemplary bone anchors include monoaxial screws,polyaxial screws, uniplanar screws, favored-angle screws, and/or any ofa variety of other bone anchor types known in the art.

Longitudinally-Adjustable Bone Anchors

FIGS. 2A-2D illustrate an exemplary embodiment of alongitudinally-adjustable bone anchor 200. The bone anchor 200 caninclude a proximal end 200 p and a distal end 200 d that define aproximal-distal or longitudinal axis A1 extending therebetween. The boneanchor 200 can be longitudinally-adjustable or expandable such that alength L of the bone anchor, defined between a distal-most tip of thebone anchor and a proximal rod seat of the bone anchor, can be modified.The bone anchor 200 can be adjustable in situ, e.g., after implanting inbone, or prior to being implanted.

The bone anchor 200 can include an anchor portion or shank 202, a heador receiver member 204, and a closure mechanism 208.

The shank 202 can include inner and outer telescoping portions 230, 232movable with respect to one another to adjust the length L of the boneanchor 200. In the illustrated embodiment, the outer telescoping portion232 includes a sleeve that defines an inner cavity 234. The cavity 234can be sized to receive at least a portion of the inner telescopingportion 230 therein. The cavity 234 can include a closed orsubstantially-closed distal end and an open proximal end. The sleeve 232can include a cannulation 236 that extends from the cavity 234 to thedistal tip of the sleeve, e.g., to allow the sleeve to be delivered overa guidewire or to allow a flowable material to be delivered through adistal tip of the sleeve and into surrounding bone. An outer surface ofthe sleeve 232 can include a bone-engaging thread 238.

The inner telescoping portion 230 can include a distal shaft 212 mountedin the cavity 234 of the sleeve 232 and a proximal head 210 to which thereceiver member 204 can be coupled. The distal shaft 212 can be slidablydisposed within the cavity 234 to allow the distal shaft to translatelongitudinally with respect to the sleeve 232. The distal shaft 212 canbe free to rotate about the axis A1 relative to the sleeve 232, orrotation between the shaft and the sleeve can be limited or completelyrestricted. Various features for restricting rotation can be used. Forexample, the sleeve 232 can include a transverse pin or a ridge that isreceived in a slot or groove formed in the shaft 212 to allow the shaftto translate longitudinally relative to the sleeve but to prevent theshaft from rotating relative to the sleeve. In other arrangements, thepin or ridge can be included in the inner shaft 212 and the slot orgroove can be formed in the outer sleeve 232. The shaft 212 can includea cannulation that extends longitudinally therethrough, e.g., to allowthe shaft to be delivered over a guidewire or to allow a flowablematerial to be delivered through the shaft and into the cavity 234 orinto bone in which the bone anchor 200 is implanted.

The bone anchor 200 can include one or more stops configured to limitthe degree to which the shaft 212 can translate longitudinally relativeto the sleeve 232. For example, the bone anchor 200 can include ashoulder, pin, or other feature at a proximal end of the sleeve 232 toprevent the shaft 212 from being removed proximally from the sleeveduring use.

The bone anchor 200 can include a locking element configured toselectively lock longitudinal movement between the shaft 212 and thesleeve 232. The locking element can be configured to prevent distalmovement of the shaft 212 relative to the sleeve 232, to preventproximal movement of the shaft relative to the sleeve, or to preventboth distal and proximal movement of the shaft relative to the sleeve.

In the illustrated embodiment, the locking element includes one or morebiased teeth 240 configured to project radially inward from the innersidewall of the cavity 234 to support the shaft 212 and prevent orresist distal movement of the shaft relative to the sleeve 232. Theteeth 240 can be attached to the sidewall of the cavity 234, for examplevia a living hinge or other joint. The teeth 240 can be biased in aradially-inward direction. Accordingly, the shaft 212 can initially holdthe teeth 240 in a retracted position and then, as the shaft is liftedproximally relative to the sleeve 232, the teeth can deploy into thecavity 234. The teeth 240 can be biased by respective leaf springs 242as shown, by resilient or shape-memory material properties of the teeth,or by any of a variety of other bias mechanisms, such as coil springsand the like. In the illustrated embodiment, the teeth 240 are deployedto engage a distal-facing surface of the shaft 212 and prevent or resistdistal movement of the shaft. In other arrangements, the teeth 240 canbe deployed into recesses formed in the sidewall of the shaft 212 toprevent or resist both proximal and distal movement, or can grip anouter surface of the shaft 212 with sufficient strength to prevent orresist both proximal and distal movement. The teeth 240 can defineunidirectional ramping surfaces, such that the teeth prevent distalmovement but allow proximal movement or vice-versa.

While biased teeth 240 are shown, it will be appreciated that variousother locking elements can be used instead or in addition. For example,a flowable material can be delivered through a cannulation of the shaft212 to fill the void space left in the cavity 234 once the shaft istranslated proximally relative to the sleeve 232. The flowable materialcan be a curable material configured to solidify within the cavity 234to lock movement between the shaft 212 and the sleeve 232. Exemplarymaterials include cements, adhesives, and the like. As another example,the sleeve 232 can include one or more spring-loaded pins configured todeploy into the cavity 234 as the shaft 212 is translated proximallyrelative to the sleeve. In some embodiments, a plurality of pins can bespaced longitudinally along the inner surface of the sleeve 232 toprovide incremental locking at a plurality of discrete points along thelength of the sleeve. As yet another example, teeth, pins, hooks, barbs,or other structures can be deployed from the shaft 212 to engage thesleeve 232 to lock movement therebetween. Such structures can be biasedradially outward from the shaft 212. Alternatively, or in addition, suchstructures can be deployed from the shaft 212 by inserting an elongatedrod through a cannulation of the shaft to push the structures out intoengagement with the sleeve 232.

The shank 202, receiver member 204, and closure mechanism 208 caninclude any of the features of the corresponding components of the boneanchor 100 described above. For example, as shown, the receiver member204 can be polyaxially coupled to the head 210 of the shank 202 and caninclude a pair of spaced apart arms 214A, 214B defining a recess 216therebetween. The closure mechanism 208 can be positionable between andcan engage the arms 214A, 214B to capture a spinal fixation element,e.g., a spinal rod 206, within the receiver member 204, to fix thespinal fixation element with respect to the receiver member, and to fixthe receiver member with respect to the shank 202.

In use, the bone anchor 200 can be initially configured such that theinner telescoping portion 230 is disposed in a distal position withrespect to the outer telescoping portion 232, as shown in FIG. 2A. Inthe initial configuration, the locking element (e.g., the deployableteeth 240) can be in a retracted or disengaged position. A driverinstrument can be applied to the head 210 of the anchor portion 202 torotate the anchor portion about the axis A1. The inner and outertelescoping portions 230, 232 can be rotationally fixed to one anotherat least in the initial configuration such that torque applied to theinner telescoping portion is in turn applied to the outer telescopingportion to drive the anchor portion 202 into bone B.

Once the anchor portion 202 is driven to the target depth, or at anyother desired time, a spinal rod 206 can be positioned in the receivermember 204 and the closure mechanism 208 can be applied to secure therod, as shown in FIG. 2B. In the illustrated embodiment, a set screw 208is threaded into extension tabs 228 that extend proximally from the arms214A, 214B of the receiver member 204.

As the set screw 208 is tightened to reduce the rod 206 into thereceiver member 204, as shown in FIG. 2C, the inner telescoping portion230 can be pulled proximally such that it translates longitudinally withrespect to the outer telescoping portion 232 while the outer telescopingportion remains at a fixed longitudinal position with respect to thesurrounding bone B. The set screw 208 can be advanced distally withinthe receiver member 204 until the rod 206 is securely fastened to thebone anchor 200, as shown in FIG. 2D, and the reduction tabs 228 can beremoved.

At any point in the above process, the locking element can be deployedor engaged to lock the relative longitudinal positions of the inner andouter telescoping portions 230, 232. The bone anchor 200 can allow thelength L of the bone anchor to be adjusted independently of adjusting anangle between the receiver member 204 and the shank 202. The bone anchor200 can allow the length L of the bone anchor to be adjusted at alocation other than the interface between the receiver member 204 andthe shank 202. The bone anchor 200 can allow the length L of the boneanchor to be adjusted, and/or can allow the rod to be moved towards thereceiver member, without disturbing the anchor-bone interface, e.g.,without moving the thread 238 relative to the bone.

It will thus be appreciated that the above process allows the length Lof the bone anchor 200 to be adjusted in situ such that the receivermember 204 can be pulled proximally towards the rod 206 instead of or inaddition to forcing the rod distally towards the receiver member. Byreducing or eliminating the need to reduce the rod 206 distally relativeto the anchor portion 202, reduction forces applied to the anchor-boneinterface can be reduced, thereby improving the strength and stabilityof the implanted construct. This can also reduce or eliminate the needto precisely contour the rod 206 to the bone anchor 200, simplifying thesurgical procedure.

FIGS. 3A-3D illustrate an exemplary embodiment of alongitudinally-adjustable bone anchor 300. The bone anchor 300 caninclude a proximal end 300 p and a distal end 300 d that define aproximal-distal or longitudinal axis A1 extending therebetween. The boneanchor 300 can be longitudinally-adjustable or expandable such that alength L of the bone anchor, defined between a distal-most tip of thebone anchor and a proximal rod seat of the bone anchor, can be modified.The bone anchor 300 can be adjustable in situ, e.g., after implanting inbone, or prior to being implanted.

The bone anchor 300 can include an anchor portion or shank 302, a heador receiver member 304, and a closure mechanism 308.

The shank 302 can include inner and outer telescoping portions 330, 332movable with respect to one another to adjust the length L of the boneanchor 300. In the illustrated embodiment, the outer telescoping portion332 includes a sleeve that defines an inner cavity 334. The cavity 334can be sized to receive at least a portion of the inner telescopingportion 330 therein. The cavity 334 can include a closed orsubstantially-closed distal end and an open proximal end. The sleeve 332can include a cannulation 336 that extends from the cavity 334 to thedistal tip of the sleeve, e.g., to allow the sleeve to be delivered overa guidewire or to allow a flowable material to be delivered through adistal tip of the sleeve and into surrounding bone. An outer surface ofthe sleeve 332 can include a bone-engaging thread 338 and an innersurface of the sleeve can include a thread 340 for engaging the innertelescoping portion 330.

The inner telescoping portion 330 can include a distal shaft 312 mountedin the cavity 334 of the sleeve 332 and a proximal head 310 to which thereceiver member 304 can be coupled. The distal shaft 312 can include anouter thread 342 engaged with the inner thread 340 of the sleeve 332 toallow the distal shaft to translate longitudinally with respect to thesleeve by rotating the shaft within the cavity 334 about the axis A1.The shaft 312 can include a cannulation that extends longitudinallytherethrough, e.g., to allow the shaft to be delivered over a guidewireor to allow a flowable material to be delivered through the shaft andinto the cavity 334 or into bone in which the bone anchor 300 isimplanted.

The bone anchor 300 can include one or more stops configured to limitthe degree to which the shaft 312 can translate longitudinally relativeto the sleeve 332. For example, the bone anchor 300 can include ashoulder, pin, or other feature at a proximal end of the sleeve 332 toprevent the shaft 312 from being removed proximally from the sleeveduring use.

The bone anchor 300 can include a locking element configured toselectively lock longitudinal movement between the shaft 312 and thesleeve 332. The locking element can be configured to prevent distalmovement of the shaft 312 relative to the sleeve 332, to preventproximal movement of the shaft relative to the sleeve, or to preventboth distal and proximal movement of the shaft relative to the sleeve.

In the illustrated embodiment, the locking element is formed by thethreaded interface between the shaft 312 and the outer sleeve 332. Itwill be appreciated, however, that other locking elements can be usedinstead or in addition. For example, a flowable material can bedelivered through a cannulation of the shaft 312 to fill the void spaceleft in the cavity 334 once the shaft is translated proximally relativeto the sleeve 332. The flowable material can be a curable materialconfigured to solidify within the cavity 334 to lock movement betweenthe shaft 312 and the sleeve 332. Exemplary materials include cements,adhesives, and the like. As another example, the sleeve 332 can includeone or more spring-loaded pins configured to deploy into the cavity 334as the shaft 312 is translated proximally relative to the sleeve. Insome embodiments, a plurality of pins can be spaced longitudinally alongthe inner surface of the sleeve 332 to provide incremental locking at aplurality of discrete points along the length of the sleeve. As yetanother example, teeth, pins, hooks, barbs, or other structures can bedeployed from the shaft 312 to engage the sleeve 332 or vice versa tolock movement therebetween. Such structures can be biased to deployautomatically or can be manually deployed, for example by an elongatedrod inserted through a cannulation of the shaft to push the structuresout into engagement with the sleeve 332.

The shank 302, receiver member 304, and closure mechanism 308 caninclude any of the features of the corresponding components of the boneanchor 100 described above. For example, as shown, the receiver member304 can be polyaxially coupled to the head 310 of the shank 302 and caninclude a pair of spaced apart arms 314A, 314B defining a recess 316therebetween. The closure mechanism 308 can be positionable between andcan engage the arms 314A, 314B to capture a spinal fixation element,e.g., a spinal rod 306, within the receiver member 304, to fix thespinal fixation element with respect to the receiver member, and to fixthe receiver member with respect to the shank 302.

In use, the bone anchor 300 can be initially configured such that theinner telescoping portion 330 is disposed in a distal position withrespect to the outer telescoping portion 332, as shown in FIG. 3A. Forexample, the shaft 312 can be threaded all the way into the sleeve 332to bottom out the shaft in the sleeve. A driver instrument can beapplied to the head 310 of the anchor portion 302 to rotate the anchorportion about the axis A1. The inner and outer telescoping portions 330,332 can be rotationally fixed to one another in at least one rotation aldirection and at least in the initial configuration such that torqueapplied to the inner telescoping portion is in turn applied to the outertelescoping portion to drive the anchor portion 302 into bone B. Forexample, bottoming out the shaft 312 in the sleeve 332 can allow torqueto be applied to the sleeve via the shaft in one rotational direction,e.g., in a clockwise or tightening direction.

Once the anchor portion 302 is driven to the target depth, or at anyother desired time, the length L of the bone anchor 300 can be adjustedto achieve optimal positioning between the receiver member 304 and aspinal rod 306. The length can be adjusted by rotating the driverinstrument in an opposite direction to back the shaft 312 out of theouter sleeve 332. The torque required to rotate the shaft 312 relativeto the sleeve 332 can be less than the torque required to loosen thesleeve 332 from the bone B, such that counter-rotation of the driver iseffective to lift the shaft proximally 312 without loosening the sleevefrom the bone. When the receiver member 304 is positioned at the desiredheight, the rod 306 can be inserted into the receiver member and theclosure mechanism 308 can be applied to secure the rod, as shown in FIG.3C. In the illustrated embodiment, a set screw 308 is threaded intoextension tabs 328 that extend proximally from the arms 314A, 314B ofthe receiver member 304 and is advanced distally within the receivermember until the rod 306 is securely fastened to the bone anchor 300, asshown in FIG. 3D, at which point the reduction tabs 328 can be removed.

The bone anchor 300 can allow the length L of the bone anchor to beadjusted independently of adjusting an angle between the receiver member304 and the shank 302. The bone anchor 300 can allow the length L of thebone anchor to be adjusted at a location other than the interfacebetween the receiver member 304 and the shank 302. The bone anchor 300can allow the length L of the bone anchor to be adjusted, and/or canallow the rod to be moved towards the receiver member, withoutdisturbing the anchor-bone interface, e.g., without moving the thread338 relative to the bone.

It will thus be appreciated that the above process allows the length Lof the bone anchor 300 to be adjusted in situ such that the receivermember 304 can be moved proximally towards the rod 306 instead of or inaddition to forcing the rod distally towards the receiver member. Byreducing or eliminating the need to reduce the rod 306 distally relativeto the anchor portion 302, reduction forces applied to the anchor-boneinterface can be reduced, thereby improving the strength and stabilityof the implanted construct. This can also reduce or eliminate the needto precisely contour the rod 306 to the bone anchor 300, simplifying thesurgical procedure.

FIGS. 4A-4C illustrate an exemplary embodiment of alongitudinally-adjustable bone anchor 400. The bone anchor 400 caninclude a proximal end 400 p and a distal end 400 d that define aproximal-distal or longitudinal axis A1 extending therebetween. The boneanchor 400 can be longitudinally-adjustable or expandable such that alength L of the bone anchor, defined between a distal-most tip of thebone anchor and a proximal rod seat of the bone anchor, can be modified.The bone anchor 400 can be adjustable in situ, e.g., after implanting inbone, or prior to being implanted.

The bone anchor 400 can include an anchor portion or shank 402, a heador receiver member 404, and a closure mechanism 408.

The shank 402 can include inner and outer telescoping portions 430, 432movable with respect to one another to adjust the length L of the boneanchor 400. In the illustrated embodiment, the outer telescoping portion432 includes a sleeve that defines a proximal inner cavity 434 p and adistal inner cavity 434 d. The proximal and distal cavities 434 p, 434 dcan be separated by an annular projection 444. The cavities 434 p, 434 dcan be sized to receive at least a portion of the inner telescopingportion 430 therein. The sleeve 432 can include a cannulation to allowthe sleeve to be delivered over a guidewire or to allow a flowablematerial to be delivered through a distal tip of the sleeve and intosurrounding bone. An outer surface of the sleeve 432 can include abone-engaging thread 438. A bias element or spring 446 configured tobias the inner telescoping portion 430 in a distal direction relative tothe outer telescoping portion 432 can be disposed in the distal cavity434 d. A series of ratchet teeth 448 or other locking features can beformed in an inner sidewall of the proximal cavity 434 p. The ratchetteeth 448 can be engaged with a locking ring 450 to selectively lock theinner telescoping portion 430 at any of a plurality of discretelongitudinal positions along the outer telescoping portion 432.

The inner telescoping portion 430 can include a shaft 412 mounted in thesleeve 432 and a proximal head 410 to which the receiver member 404 canbe coupled. The shaft 412 can be slidably disposed within the cavity 434to allow the shaft to translate longitudinally with respect to thesleeve 432. The shaft 412 can be free to rotate about the axis A1relative to the sleeve 432, or rotation between the shaft and the sleevecan be limited or completely restricted. Various features forrestricting rotation can be used. For example, the sleeve 432 caninclude a transverse pin or a ridge that is received in a slot or grooveformed in the shaft 412 to allow the shaft to translate longitudinallyrelative to the sleeve but to prevent the shaft from rotating relativeto the sleeve. In other arrangements, the pin or ridge can be includedin the inner shaft 412 and the slot or groove can be formed in the outersleeve 432. The shaft 412 can include a cannulation that extendslongitudinally therethrough, e.g., to allow the shaft to be deliveredover a guidewire or to allow a flowable material to be delivered throughthe shaft and into the cavity 434 or into bone in which the bone anchor400 is implanted.

The shaft 412 can include a proximal portion 412 p and a distal portion412 d. The proximal and distal portions 412 p, 412 d can be formedintegrally with one another or can be separate components joinedtogether using any of a variety of known techniques such as an adhesive,a weld, a threaded interface, and so forth. The proximal shaft 412 p canbe slidably disposed in the proximal cavity 434 p. Distal travel of theproximal shaft 412 p relative to the sleeve 432 can be limited by theprojection 444.

The distal shaft 412 d can include a reduced-diameter proximal portionconfigured to slide through a central aperture defined by the projection444 and an enlarged-diameter distal portion configured to abut theprojection 444 to limit proximal movement of the shaft 412 relative tothe sleeve 432, e.g., to prevent the shaft from being removed proximallyfrom the sleeve during use. The bias element 446 can be disposed betweenthe projection 444 and a shoulder 448 formed on the distal shaft 412 d.The bias element 446 can be effective to bias the distal shaft 412 d,and the proximal shaft 412 p attached thereto, distally relative to theouter sleeve 432. This can help prevent inadvertent longitudinalextension of the bone anchor 400, e.g., during shipping, sterilization,or handling prior to surgery.

The bone anchor 400 can include a locking element configured toselectively lock longitudinal movement between the shaft 412 and thesleeve 432. The locking element can be configured to prevent distalmovement of the shaft 412 relative to the sleeve 432, to preventproximal movement of the shaft relative to the sleeve, or to preventboth distal and proximal movement of the shaft relative to the sleeve.

In the illustrated embodiment, the locking element includes a ring 450seated within an annular groove 452 formed in an outer surface of theproximal shaft 412 p and corresponding ratchet teeth 448 formed in thesleeve 432. The ring 450 can protrude from the groove 452 to engage theratchet teeth 448 formed in the proximal cavity 434 p.

A proximally-directed force applied along the axis A1 can cause theshaft 412 to translate longitudinally relative to the sleeve 432. As theshaft 412 slides within the sleeve, the ring 450 can slide along aninclined surface of the ratchet tooth with which it is presentlyengaged, eventually snapping into an adjacent recess formed by the nextsuccessive ratchet tooth. The ring 450 can be configured to deform orcompress radially-inward towards the groove 452 during this process. Forexample, the ring 450 can be a C-clip or can include slits, grooves, orwebbing to facilitate radial deformation. Alternatively, or in addition,the ratchet teeth 448 or the sleeve 432 can deform or expand. The aboveprocess can be repeated any number of times as desired by the user toselectively position and lock the inner shaft 412 at any of a pluralityof discrete longitudinal positions along the outer sleeve 432, therebyadjusting the length L of the bone anchor 400.

While the ring 450 and the teeth 448 are formed at a proximal end of theanchor portion 402, it will be appreciated that they can alternativelybe formed at a distal end thereof or at any location along the length ofthe anchor portion 402. The illustrated teeth 448 define unidirectionalramping surfaces, such that the teeth prevent distal movement of theshaft 412 but allow proximal movement when sufficient force is appliedthereto to deform the ring 450. In other embodiments, the teeth can beramped in an opposite direction, or can be ramped in both directions.

While a locking ring 450 and ratchet teeth 448 are shown, it will beappreciated that various other locking elements can be used instead orin addition. For example, a flowable material can be delivered through acannulation of the shaft 412 to fill the void space left in the cavity434 once the shaft is translated proximally relative to the sleeve 432.The flowable material can be a curable material configured to solidifywithin the cavity 434 to lock movement between the shaft 412 and thesleeve 432. Exemplary materials include cements, adhesives, and thelike. As another example, the sleeve 432 can include one or morespring-loaded pins configured to deploy into the cavity 434 as the shaft412 is translated proximally relative to the sleeve. In someembodiments, a plurality of pins can be spaced longitudinally along theinner surface of the sleeve 432 to provide incremental locking at aplurality of discrete points along the length of the sleeve. As yetanother example, teeth, pins, hooks, barbs, or other structures can bedeployed from the shaft 412 to engage the sleeve 432 to lock movementtherebetween. Such structures can be biased radially outward from theshaft 412. Alternatively, or in addition, such structures can bedeployed from the shaft 412 by inserting an elongated rod through acannulation of the shaft to push the structures out into engagement withthe sleeve 432.

The shank 402, receiver member 404, and closure mechanism 408 caninclude any of the features of the corresponding components of the boneanchor 100 described above. For example, as shown, the receiver member404 can be polyaxially coupled to the head 410 of the shank 402 and caninclude a pair of spaced apart arms 414A, 414B defining a recess 416therebetween. The closure mechanism 408 can be positionable between andcan engage the arms 414A, 414B to capture a spinal fixation element,e.g., a spinal rod 406, within the receiver member 404, to fix thespinal fixation element with respect to the receiver member, and to fixthe receiver member with respect to the shank 402.

In use, the bone anchor 400 can be initially configured such that theinner telescoping portion 430 is disposed in a distal position withrespect to the outer telescoping portion 432, as shown in FIG. 4A. Inthe initial configuration, the locking ring 450 can be seated in arelatively distal position along the length of the ratchet teeth 448. Adriver instrument can be applied to the head 410 of the anchor portion402 to rotate the anchor portion about the axis A1. The inner and outertelescoping portions 430, 432 can be rotationally fixed to one anotherat least in the initial configuration such that torque applied to theinner telescoping portion is in turn applied to the outer telescopingportion to drive the anchor portion 402 into bone B.

Once the anchor portion 402 is driven to the target depth, or at anyother desired time, a spinal rod 406 can be positioned in the receivermember 404 and the closure mechanism 408 can be applied to secure therod, as shown in FIG. 4A. In the illustrated embodiment, a set screw 408is threaded into the arms 414A, 414B of the receiver member 404.

As the set screw 408 is tightened to reduce the rod 406 into thereceiver member 404, the inner telescoping portion 430 can be pulledproximally such that it translates longitudinally with respect to theouter telescoping portion 432 while the outer telescoping portionremains at a fixed longitudinal position with respect to the surroundingbone B. As the inner telescoping portion 430 moves proximally, thelocking ring 450 traverses one or more of the ratchet teeth 448,snapping into engagement with each successive groove defined between theteeth. The set screw 408 can be advanced distally within the receivermember 404 until the rod 406 is securely fastened to the bone anchor400. The shaft 412 at this time is disposed in a final position alongthe sleeve 432, locked from translating distally by the interactionbetween the ring 450 and the teeth 448.

The bone anchor 400 can allow the length L of the bone anchor to beadjusted independently of adjusting an angle between the receiver member404 and the shank 402. The bone anchor 400 can allow the length L of thebone anchor to be adjusted at a location other than the interfacebetween the receiver member 404 and the shank 402. The bone anchor 400can allow the length L of the bone anchor to be adjusted, and/or canallow the rod to be moved towards the receiver member, withoutdisturbing the anchor-bone interface, e.g., without moving the thread438 relative to the bone.

It will thus be appreciated that the above process allows the length Lof the bone anchor 400 to be adjusted in situ such that the receivermember 404 can be pulled proximally towards the rod 406 instead of or inaddition to forcing the rod distally towards the receiver member. Byreducing or eliminating the need to reduce the rod 406 distally relativeto the anchor portion 402, reduction forces applied to the anchor-boneinterface can be reduced, thereby improving the strength and stabilityof the implanted construct. This can also reduce or eliminate the needto precisely contour the rod 406 to the bone anchor 400, simplifying thesurgical procedure.

FIGS. 5A-5F illustrate an exemplary embodiment of alongitudinally-adjustable bone anchor 500. The bone anchor 500 caninclude a proximal end 500 p and a distal end 500 d that define aproximal-distal or longitudinal axis A1 extending therebetween. The boneanchor 500 can be longitudinally-adjustable or expandable such that alength L of the bone anchor, defined between a distal-most tip of thebone anchor and a proximal rod seat of the bone anchor, can be modified.The bone anchor 500 can be adjustable in situ, e.g., after implanting inbone, or prior to being implanted.

The bone anchor 500 can include an anchor portion or shank 502, a heador receiver member 504, and a closure mechanism 508.

The shank 502 can include inner and outer telescoping portions 530, 532movable with respect to one another to adjust the length L of the boneanchor 500. In the illustrated embodiment, the outer telescoping portion532 includes a sleeve that defines an inner cavity 534. The cavity 534can be sized to receive at least a portion of the inner telescopingportion 530 therein. The cavity 534 can include a closed orsubstantially-closed distal end and an open proximal end. The sleeve 532can include a cannulation 536 that extends from the cavity 534 to thedistal tip of the sleeve, e.g., to allow the sleeve to be delivered overa guidewire or to allow a flowable material to be delivered through adistal tip of the sleeve and into surrounding bone. An outer surface ofthe sleeve 532 can include a bone-engaging thread 538.

The inner telescoping portion 530 can include a distal shaft 512 mountedin the cavity 534 of the sleeve 532 and a proximal head 510 to which thereceiver member 504 can be coupled. The distal shaft 512 can be slidablydisposed within the cavity 534 to allow the distal shaft to translatelongitudinally with respect to the sleeve 532. The distal shaft 512 canbe free to rotate about the axis A1 relative to the sleeve 532, orrotation between the shaft and the sleeve can be limited or completelyrestricted. Various features for restricting rotation can be used. Forexample, the sleeve 532 can include a transverse pin or a ridge that isreceived in a slot or groove formed in the shaft 512 to allow the shaftto translate longitudinally relative to the sleeve but to prevent theshaft from rotating relative to the sleeve. In other arrangements, thepin or ridge can be included in the inner shaft 512 and the slot orgroove can be formed in the outer sleeve 532. The shaft 512 can includea cannulation that extends longitudinally therethrough, e.g., to allowthe shaft to be delivered over a guidewire or to allow a flowablematerial to be delivered through the shaft and into the cavity 534 orinto bone in which the bone anchor 500 is implanted.

The bone anchor 500 can include one or more stops configured to limitthe degree to which the shaft 512 can translate longitudinally relativeto the sleeve 532. For example, the bone anchor 500 can include ashoulder, pin, or other feature at a proximal end of the sleeve 532 toprevent the shaft 512 from being removed proximally from the sleeveduring use.

The bone anchor 500 can include a locking element configured toselectively lock longitudinal movement between the shaft 512 and thesleeve 532. The locking element can be configured to prevent distalmovement of the shaft 512 relative to the sleeve 532, to preventproximal movement of the shaft relative to the sleeve, or to preventboth distal and proximal movement of the shaft relative to the sleeve.

In the illustrated embodiment, the locking element includes one or moretabs 540 configured to lock relative movement between the shaft 512 andthe sleeve 532 when a distally-directed force is applied thereto, e.g.,by tightening a set screw 508. Each tab 540 can have a proximal end anda distal end aligned generally parallel with the axis A1. The proximalend of the tab 540 can project into the rod recess 516 of the receivermember 504 such that the tab interferes with the set screw 508 as theset screw is tightened. The tab 540 can extend through an opening formedin the respective arm 514A, 514B of the receiver member such that thedistal end of the tab is positioned outside of the rod recess 516.Instead of extending through an opening in the receiver member 504, thetabs 540 can be disposed entirely on the exterior of the receiver member504 and can be engaged with an alternative closure mechanism, such as anut that extends around the outer circumference of the receiver member.The distal end of the tab 540 can engage with the shaft 512, the sleeve532, or both the shaft and the sleeve to lock one or more motion degreesof freedom between the shaft and the sleeve.

For example, the distal end of the tab 540 can be tapered in aproximal-distal direction to define a wedge that is at least partiallyinserted between the shaft 512 and the sleeve 532. As the set screw 508is tightened, each tab 540 can translate distally to drive the wedgedeeper between the shaft and the sleeve to lock movement between saidcomponents.

As another example, the distal end of the tab 540 can be initiallyfolded, bent, or deformed radially-inward, as shown in FIGS. 5A and 5B.Resilient or shape memory material properties of the tabs 540 can causethe tabs to be biased away from the folded position towards a deployedposition shown in FIGS. 5C and 5D. Accordingly, as the receiver member504 and shaft 512 are lifted proximally relative to the sleeve 532, thetabs 540 can spring down from the folded position to contact aproximal-facing surface of the sleeve 532 and act as vertical supportsto maintain the receiver member 504 at an elevated position relative tothe sleeve 532. In another arrangement, a force applied to the proximalend of the tab 540 by the set screw 508 can release the tab 540 from thefolded position and allow it to spring into the deployed position.

While opposed tabs 540 are shown, it will be appreciated that variousother locking elements can be used instead or in addition. For example,a flowable material can be delivered through a cannulation of the shaft512 to fill the void space left in the cavity 534 once the shaft istranslated proximally relative to the sleeve 532. The flowable materialcan be a curable material configured to solidify within the cavity 534to lock movement between the shaft 512 and the sleeve 532. Exemplarymaterials include cements, adhesives, and the like. As another example,the sleeve 532 can include one or more spring-loaded pins configured todeploy into the cavity 534 as the shaft 512 is translated proximallyrelative to the sleeve. In some embodiments, a plurality of pins can bespaced longitudinally along the inner surface of the sleeve 532 toprovide incremental locking at a plurality of discrete points along thelength of the sleeve. As yet another example, teeth, pins, hooks, barbs,or other structures can be deployed from the shaft 512 to engage thesleeve 532 to lock movement therebetween. Such structures can be biasedradially outward from the shaft 512. Alternatively, or in addition, suchstructures can be deployed from the shaft 512 by inserting an elongatedrod through a cannulation of the shaft to push the structures out intoengagement with the sleeve 532.

The shank 502, receiver member 504, and closure mechanism 508 caninclude any of the features of the corresponding components of the boneanchor 100 described above. For example, as shown, the receiver member504 can be polyaxially coupled to the head 510 of the shank 502 and caninclude a pair of spaced apart arms 514A, 514B defining a recess 516therebetween. The closure mechanism 508 can be positionable between andcan engage the arms 514A, 514B to capture a spinal fixation element,e.g., a spinal rod 506, within the receiver member 504, to fix thespinal fixation element with respect to the receiver member, and to fixthe receiver member with respect to the shank 502.

In use, the bone anchor 500 can be initially configured such that theinner telescoping portion 530 is disposed in a distal position withrespect to the outer telescoping portion 532, as shown in FIG. 5A. Inthe initial configuration, the locking element (e.g., the tabs 540) canbe in a retracted or disengaged position. A driver instrument can beapplied to the head 510 of the anchor portion 502 to rotate the anchorportion about the axis A1. The inner and outer telescoping portions 530,532 can be rotationally fixed to one another at least in the initialconfiguration such that torque applied to the inner telescoping portionis in turn applied to the outer telescoping portion to drive the anchorportion 502 into bone B.

Once the anchor portion 502 is driven to the target depth, or at anyother desired time, a spinal rod 506 can be positioned in the receivermember 504 and the closure mechanism 508 can be applied to secure therod, as shown in FIG. 5B. In the illustrated embodiment, a set screw 508is threaded into extension tabs 528 that extend proximally from the arms514A, 514B of the receiver member 504.

As the set screw 508 is tightened to reduce the rod 506 into thereceiver member 504, as shown in FIG. 5C, the inner telescoping portion530 can be pulled proximally such that it translates longitudinally withrespect to the outer telescoping portion 532 while the outer telescopingportion remains at a fixed longitudinal position with respect to thesurrounding bone B. The set screw 508 can be advanced distally withinthe receiver member 504 until the rod 506 is securely fastened to thebone anchor 500, as shown in FIG. 5D, and the reduction tabs 528 can beremoved. As the set screw 508 is tightened, the locking element (e.g.,the tabs 540) can be deployed or engaged to lock the relativelongitudinal positions of the inner and outer telescoping portions 530,532.

The bone anchor 500 can allow the length L of the bone anchor to beadjusted independently of adjusting an angle between the receiver member504 and the shank 502. The bone anchor 500 can allow the length L of thebone anchor to be adjusted at a location other than the interfacebetween the receiver member 504 and the shank 502. The bone anchor 500can allow the length L of the bone anchor to be adjusted, and/or canallow the rod to be moved towards the receiver member, withoutdisturbing the anchor-bone interface, e.g., without moving the thread538 relative to the bone.

It will thus be appreciated that the above process allows the length Lof the bone anchor 500 to be adjusted in situ such that the receivermember 504 can be pulled proximally towards the rod 506 instead of or inaddition to forcing the rod distally towards the receiver member. Byreducing or eliminating the need to reduce the rod 506 distally relativeto the anchor portion 502, reduction forces applied to the anchor-boneinterface can be reduced, thereby improving the strength and stabilityof the implanted construct. This can also reduce or eliminate the needto precisely contour the rod 506 to the bone anchor 500, simplifying thesurgical procedure.

FIGS. 6A-6D illustrate an exemplary embodiment of alongitudinally-adjustable bone anchor 600, shown with a spinal rod 606.The bone anchor 600 can include a proximal end 600p and a distal end600d that define a proximal-distal or longitudinal axis A1 extendingtherebetween. The bone anchor 600 can be longitudinally-adjustable orexpandable such that a length L of the bone anchor, defined between adistal-most tip of the bone anchor and a proximal rod seat of the boneanchor, can be modified. The bone anchor 600 can be adjustable in situ,e.g., after implanting in bone, or prior to being implanted.

The bone anchor 600 can include an anchor portion or shank 602, a heador receiver member 604, a closure mechanism 608, and one or more spacersor risers 654. In use, the spacer 654 can be positioned in the receivermember 604 to increase the height of the rod seat and thereby extend thelength L of the bone anchor 600.

The shank 602, receiver member 604, and closure mechanism 608 caninclude any of the features of the corresponding components of the boneanchor 100 described above. For example, as shown, the receiver member604 can be polyaxially coupled to the head 610 of the shank 602 and caninclude a pair of spaced apart arms 614A, 614B defining a recess 616therebetween. The closure mechanism 608 can be positionable between andcan engage the arms 614A, 614B to capture a spinal fixation element,e.g., a spinal rod 606, within the receiver member 604, to fix thespinal fixation element with respect to the receiver member, and to fixthe receiver member with respect to the shank 602.

The spacer 654 can extend across at least a portion of the rod seat ofthe receiver member 604. The spacer 654 can include a distal facingsurface 654 d that mimics the distal facing surface of a spinal fixationor stabilization element with which the bone anchor assembly 600 is tobe used. For example, in the case of a cylindrical spinal rod 606, thedistal-facing surface 654 d of the spacer 654 can define a section of acylinder having a radius equal to or substantially equal to the diameterof the spinal rod. The proximal-facing surface 654 p of the spacer 654can define a seat configured to receive the spinal fixation orstabilization element therein. In the illustrated embodiment, the seat654 p is sized and shaped to receive a cylindrical spinal rod 606therein. The radius of curvature of the proximal-facing seat 654 p canbe equal to or substantially equal to that of the rod-receiving channel616 of the receiver member 604.

The spacer 654 can include features for preventing movement of thespacer with respect to the receiver member 604 in one or more degrees offreedom. For example, as shown, the spacer can include one or moreprotrusions 656 that engage an outer sidewall of the receiver member 604to prevent translation of the spacer 654 along a rod or spacer axis A2with respect to the receiver member. The protrusions 656 can extend fromthe distal-facing surface 654 d of the spacer 654 as shown, or canextend from side surfaces of the spacer or any other surface of thespacer. The protrusions 656 can be convexly curved as shown to eliminatesharp edges that could irritate surrounding tissue. The protrusions 656can include inwardly-facing planar surfaces 658 that engagecorresponding outwardly-facing planar surfaces 660 of the receivermember 604. Alternatively, or in addition, the spacer 654 can includeprotrusions that engage an inner surface of the receiver member 604, orother features for preventing or limiting axial translation of thespacer relative to the receiver member along the axis A2. In someembodiments, the spacer 654 can include features for limiting orpreventing rotation of the spacer relative to the receiver member 604about the axis A2. For example, at least a portion 662 of the sidewallsof the spacer 654 can be planar and can engage corresponding planarportions 664 of the rod-receiving recess 616 of the receiver member 604to prevent rotation of the spacer about the axis A2 relative to thereceiver member. The spacer 654 can be snap-fit, friction-fit, orotherwise reversibly mated to the receiver member 604, e.g., to helpretain the spacer 654 in place prior to inserting and locking the rod606.

When the bone anchor 600 is assembled, the spacer can be positionedbetween the opposed arms 614A, 614B of the receiver member 604 such thatthe spacer 654 is seated within the rod-receiving recess 616 of thereceiver member. The spinal rod 606 can then be seated on theproximal-facing surface 654 p of the spacer 654, between the opposedarms 614A, 614B of the receiver member 604, and locked in place with theclosure mechanism 608 as described above.

A kit can be provided including a plurality of spacers 654, each havinga different height in the proximal-distal direction, or each having adifferent rod-seat radius, etc., to give the user flexibility inselecting the length L of the bone anchor 600 and the diameter of therod with which the bone anchor 600 is used. FIG. 6B illustrates a spacer654 having a height H1 and FIG. 6C illustrates a spacer 654′ having aheight H2 that is greater than H1.

In some cases, the thickness of the spacer 654 can cause the spinal rod606 to be raised up within the receiver member 604 to a degree thatprevents sufficient attachment of the closure mechanism 608 or preventsattachment of the closure mechanism altogether. In such cases, the boneanchor assembly 600 can include a cap 666, e.g., of the type shown inFIG. 6D. The cap 666 can attach to the proximal end of the receivermember 604. The cap 666 can include a threaded central opening sized toreceive the closure mechanism 608. Accordingly, the cap 666 canfunctionally extend the height of the threaded portion of the receivermember 604 to accommodate both the rod 606 and the spacer 654 betweenthe rod seat of the receiver member 604 and the closure mechanism 608.The illustrated cap 666 includes a generally U-shaped channel sized toaccommodate the spinal rod 606 defined by opposed arms 668A, 668B. Thecap 666 can be attached to the receiver member 604 in any of a varietyof ways. For example, the cap 666 can include one or more projections,e.g., formed on an inner surface of the arms 668A, 668B that engage witha corresponding one or more recesses formed in the receiver member 604,or the receiver member can include one or more projections that engagewith a corresponding one or more recesses formed in the cap. As theclosure mechanism 608 is tightened, the middle portion of the cap 666can flex proximally, pulling projections formed on inner surface of thearms 668A, 668B tightly into engagement with the receiver member 604.The cap 666 can snap fit onto the receiver member 604. The cap 666 canslide onto the receiver member 604 from the side with a tongue andgroove or dovetail connection. The cap 666 can lock onto the receivermember 604 by a quarter-turn rotation of the cap relative to thereceiver member. The distal-facing underside of the cap 666 can form anegative of the proximal end of the receiver member 604 to limit orprevent rotation of the cap relative to the receiver member about theaxis A1. The proximal-facing surface of the cap 666 can be convexlycurved or domed to eliminate sharp edges that could irritate surroundingtissue.

In use, the bone anchor 600 can be implanted in bone using standardtechniques. A driver instrument can be applied to the head 610 of theanchor portion 602 to rotate the anchor portion about the axis A1 anddrive the anchor portion into bone B.

Once the anchor portion 602 is driven to the target depth, or at anyother desired time, a spacer 654 and a spinal rod 606 can be positionedin the receiver member 604 and the closure mechanism 608 can be appliedto secure the spacer and the rod, as shown in FIG. 6A. This process caninclude test fitting the rod 606 to the bone anchor 600 and determiningan optimal spacer height. A spacer 654 that most closely matches thedetermined height can be selected from among a plurality of spacers,e.g., provided as part of a kit. As another example, a plurality ofspacers having different heights can be test fit to the bone anchor 600until the desired bone anchor length L is achieved. In some embodiments,multiple spacers can be stacked on top of one another within thereceiver member 604 to achieve the desired bone anchor length L. In someembodiments, the spacers can be formed from a trimmable or shavablematerial to allow the height of the spacer to be adjusted or fine-tunedduring the surgical procedure. Exemplary spacer materials include metalssuch as titanium, polymers such as PEEK, elastomers such as silicone,materials known to be biocompatible or suitable for surgicalapplications, and/or any of a variety of other materials. The spacer 654can have a height H measured between the proximal and distal surfaces654 p, 654 d in the range of about 0.5 mm to about 50 mm, in the rangeof about 1 mm to about 10 mm, and/or in the range of about 1 mm to about5 mm. The spacer can have a height H of about 5 mm, about 4 mm, about 3mm, about 2 mm, or about 1 mm. The ratio of the height of the spacer tothe length of the shank portion 602 can be in the range of about 5% toabout 100%, in the range of about 10% to about 50%, and/or in the rangeof about 15% to about 30%.

With the spinal rod 606 and the desired spacer 654 assembled to thereceiver member 604, the set screw 608 can be advanced distally withinthe receiver member 604 until the rod 606 is securely fastened to thebone anchor 600.

The bone anchor 600 can allow the length L of the bone anchor to beadjusted independently of adjusting an angle between the receiver member604 and the shank 602. The bone anchor 600 can allow the length L of thebone anchor to be adjusted at a location other than the interfacebetween the receiver member 604 and the shank 602. The bone anchor 600can allow the length L of the bone anchor to be adjusted, and/or canallow the rod to be seated in the receiver member, without disturbingthe anchor-bone interface, e.g., without moving a thread of the anchorportion 602 relative to the bone.

It will thus be appreciated that the above process allows the length Lof the bone anchor 600 to be adjusted in situ such that the effectiveheight of the receiver member 604 can be moved or adjusted proximallytowards the rod 606 instead of or in addition to forcing the roddistally towards the receiver member. By reducing or eliminating theneed to reduce the rod 606 distally relative to the anchor portion 602,reduction forces applied to the anchor-bone interface can be reduced,thereby improving the strength and stability of the implanted construct.This can also reduce or eliminate the need to precisely contour the rod606 to the bone anchor 600, simplifying the surgical procedure.

It should be noted that any ordering of method steps expressed orimplied in the description above or in the accompanying drawings is notto be construed as limiting the disclosed methods to performing thesteps in that order. Rather, the various steps of each of the methodsdisclosed herein can be performed in any of a variety of sequences. Inaddition, as the described methods are merely exemplary embodiments,various other methods that include additional steps or include fewersteps are also within the scope of the present disclosure.

The bone anchors 200, 300, 400, 500, 600 disclosed herein can belongitudinally-adjustable over a variety of lengths L. In someembodiments, the bone anchors can be longitudinally-extended by a lengthin the range of about 0.5 mm to about 50 mm, in the range of about 1 mmto about 10 mm, and/or in the range of about 1 mm to about 5 mm. Thebone anchors can be longitudinally-extended by a length about 5 mm,about 4 mm, about 3 mm, about 2 mm, or about 1 mm. The ratio of theamount by which the length of the bone anchors can be extended to thenon-extended length of the shank portion can be in the range of about 5%to about 100%, in the range of about 10% to about 50%, and/or in therange of about 15% to about 30%.

While the methods illustrated and described herein generally involveattaching spinal rods to multiple vertebrae, it will be appreciated thatthe bone anchors herein can be used with various other types of fixationor stabilization hardware, in any bone, in non-bone tissue, or innon-living or non-tissue objects. The bone anchors disclosed herein canbe fully implanted, or can be used as part of an external fixation orstabilization system. The devices and methods disclosed herein can beused in minimally-invasive surgery and/or open surgery.

The devices disclosed herein and the various component parts thereof canbe constructed from any of a variety of known materials. Exemplarymaterials include those which are suitable for use in surgicalapplications, including metals such as stainless steel, titanium, oralloys thereof, polymers such as PEEK, ceramics, carbon fiber, and soforth. The various components of the devices disclosed herein can berigid or flexible. One or more components or portions of the device canbe formed from a radiopaque material to facilitate visualization underfluoroscopy and other imaging techniques, or from a radiolucent materialso as not to interfere with visualization of other structures. Exemplaryradiolucent materials include carbon fiber and high-strength polymers.

Although specific embodiments are described above, it should beunderstood that numerous changes may be made within the spirit and scopeof the concepts described.

1. A longitudinally-adjustable bone anchor, comprising: a receivermember that defines a rod-receiving recess; a shank having inner andouter telescoping portions, the outer telescoping portion of the shankincluding a bone-engaging thread and defining an inner cavity, the innertelescoping portion including a shaft disposed in the cavity of theouter telescoping portion and a head that movably couples the shank tothe receiver member; wherein the inner and outer telescoping portionsare longitudinally-adjustable relative to one another to adjust a lengthof the bone anchor.
 2. The bone anchor of claim 1, wherein the innertelescoping portion is constrained from rotating axially relative to theouter telescoping portion.
 3. The bone anchor of claim 1, wherein theinner telescoping portion is threaded into the cavity of the outertelescoping portion.
 4. The bone anchor of claim 1, further comprising alocking element configured to selectively prevent distal movement of theinner telescoping portion relative to the outer telescoping portion, toprevent proximal movement of the inner telescoping portion relative tothe outer telescoping portion, or to prevent both proximal and distalmovement of the inner telescoping portion relative to the outertelescoping portion.
 5. The bone anchor of claim 4, wherein the lockingelement comprises one or more biased teeth configured to projectradially inward from an inner sidewall of the cavity to engage the shaftas the shaft is moved proximally within the cavity.
 6. The bone anchorof claim 4, wherein the locking element comprises a threaded engagementbetween the inner and outer telescoping portions.
 7. The bone anchor ofclaim 4, wherein the locking element comprises a locking ring disposedaround the shaft of the inner telescoping portion and configured toengage ratchet teeth spaced longitudinally along an inner surface of thecavity.
 8. The bone anchor of claim 1, wherein the cavity includesproximal and distal portions separated by an annular projection.
 9. Thebone anchor of claim 8, wherein the shaft is biased distally relative tothe outer telescoping portion by a spring disposed between the annularprojection and a shoulder formed on the shaft.
 10. The bone anchor ofclaim 4, wherein the locking element comprises one or more tabsextending from the receiver member.
 11. The bone anchor of claim 10,wherein the tabs are configured to wedge between the inner and outertelescoping portions when a distally-directed force is applied to thetabs.
 12. The bone anchor of claim 10, wherein tightening a closuremechanism to the receiver member applies a distally-directed force tothe tabs.
 13. The bone anchor of claim 10, wherein each of the tabs hasa folded position and a deployed position, the tabs in the deployedposition being configured to contact the outer telescoping portion andsupport the receiver member in an elevated position relative to theouter telescoping portion.
 14. A longitudinally-adjustable bone anchor,comprising: a receiver member that defines a rod-receiving channelhaving a first rod seat; a threaded shank movably coupled to thereceiver member; and a spacer disposed in the rod-receiving channel ofthe receiver member and having a distal surface that contacts the firstrod seat and a proximal surface that defines a second rod seat spaced adistance apart from the first rod seat.
 15. The bone anchor of claim 14,wherein the first rod seat is defined by opposed U-shaped recessesformed in the receiver member.
 16. The bone anchor of claim 14, whereinthe distal surface of the spacer is a section of a cylinder.
 17. Thebone anchor of claim 14, wherein the proximal surface of the spacer is asection of a cylinder.
 18. The bone anchor of claim 14, wherein thespacer includes one or more protrusions that engage an outer sidewall ofthe receiver member to prevent translation of the spacer relative to thereceiver member along a longitudinal axis of the spacer.
 19. The boneanchor of claim 18, wherein the protrusions extend from the distalsurface of the spacer.
 20. The bone anchor of claim 18, wherein theprotrusions are convexly curved.
 21. The bone anchor of claim 18,wherein the protrusions include inwardly-facing planar surfaces thatengage corresponding outwardly-facing planar surfaces of the receivermember.
 22. The bone anchor of claim 14, wherein the spacer includesopposed planar sidewalls connecting the proximal and distal surfaces ofthe spacer that engage respective opposed planar sidewalls of therod-receiving channel.
 23. A bone fixation method, comprising:implanting a bone anchor in a bone of a patient, the bone anchor havinga proximal portion that includes a rod seat configured to receive afixation rod therein and a distal portion configured to engage bone, thebone anchor having a length L defined between the rod seat and adistal-most tip of the bone anchor; positioning a fixation rod withrespect to the bone anchor such that the fixation rod is offsetproximally from the rod seat; and extending the length L of the boneanchor to reduce the offset between the fixation rod and the rod seat.24. The method of claim 23, wherein the length L is adjustedindependently of adjusting a position of the distal portion of the boneanchor relative to the bone.
 25. The method of claim 23, wherein thedistal portion of the bone anchor includes a thread that is threadedinto the bone and wherein the length L is adjusted without moving thethread relative to the bone.
 26. The method of claim 23, wherein thelength L is adjusted independently of adjusting an angle between theproximal and distal portions of the bone anchor.
 27. The method of claim23, wherein the length L is adjusted at a location other than aninterface between the proximal and distal portions of the bone anchor.28. The method of claim 23, wherein the distal portion of the boneanchor includes inner and outer telescoping portions and whereinadjusting the length L comprises moving the inner telescoping portionproximally relative to the outer telescoping portion.
 29. The method ofclaim 28, further comprising locking at least one of proximal movement,distal movement, and both proximal and distal movement of the innertelescoping portion relative to the outer telescoping portion via alocking element.
 30. The method of claim 29, wherein the locking elementcomprises at least one of: biased teeth configured to deploy from acavity of the outer telescoping portion to engage the inner telescopingportion; a threaded engagement between the inner and outer telescopingportions; a locking ring disposed around the inner telescoping portionand engaged with ratchet teeth formed in a cavity of the outertelescoping portion; tabs configured to wedge between the inner andouter telescoping portions when a distally-directed force is applied tothe tabs; and tabs having a folded position and a deployed position, thetabs in the deployed position being configured to contact the outertelescoping portion and support the proximal portion of the bone anchorin an elevated position relative to the outer telescoping portion. 31.The method of claim 23, wherein adjusting the length L comprisesinserting a spacer between the rod and the proximal portion of thereceiver member, the rod seat being defined by a proximal surface of thespacer.
 32. The method of claim 31, further comprising selecting thespacer from a kit of a plurality of spacers, each of the plurality ofspacers having a different height and the selected spacer having aheight corresponding to a desired degree of extension of the length L.